Ferritic stainless steel has been widely utilized in various industrial fields such as house wares, parts of motorcars, etc., as a material excellent in the corrosion resistance and the heat resistance.
The ferritic stainless steel is inexpensive as compared with an austenitic stainless steel containing a large amount of Ni but in general, is inferior in the workability and, for example, when press working is applied to a ferritic stainless steel, a surface defect called ridging is liable to cause, thereby the ferritic stainless steel is unsuitable for the use of being applied with a strong work such as a deep drawing work, etc.
Also, a ferritic stainless steel has the problems that the anisotropy (.DELTA.r) of a plastic strain ratio is large and a nonuniform deformation is liable to cause at deep drawing work.
Now, for solving the above-described problems, many attempts have hitherto been made. First, various improvements of an anti-ridging property are proposed in (a) Patent Publication (unexamined) No. 52-24913, (b) Patent Publication (unexamined) No. 56-123356, (c) Patent Publication (unexamined) No. 7-18385, (d) Patent Publication (unexamined) No. 9-53155, etc.
The stainless steel of the above-described (a) contains from 0.03 to 0.08 wt. % C, not more than 0.01 wt. % N, not more than 0.008 wt. % S, not more than 0.03 wt. % P, not more than 0.4 wt. % Si, not more than 0.5 wt. % Mn, not more than 0.3 wt. % Ni, from 15 to 20 wt. % Cr, and from 2.times.N to 0.2 wt. % Al.
The stainless steel of the above-described (b) contains not more than 0.1 wt. % C, not more than 1.0 wt. % Si, not more than 0.75 wt. % Mn, from 10 to 30 wt. % Cr, not more than 0.5 wt. % Ni, not more than 0.025 wt. % N, and from 2 to 30 ppm of B or further containing one or more kinds from 0.005 to 0.4 wt. % Al, from 0.005 to 0.6 wt. % Ti, from 0.005 to 0.4 wt. % Nb, from 0.005 to 0.4 wt. % V, from 0.005 to 0.4 wt. % Zr, from 0.02 to 0.5 wt. % Cu, not more than 0.05 wt. % Ca, and not more than 0.05 wt. % Ce.
In the stainless steel of the above-described (c), the content of Cr is from 3 to 60 wt. %, the contents of C, S, and O are reduced, and the content of N is from 0.03 to 0.5 wt. %.
The stainless steel of the above-described (d) contains not more than 0.01 wt. % C, not more than 1.0 wt. % Si, not more than 1.0 wt. % Mn, not more than 0.01 wt. % S, from 9 to 50 wt. % Cr, not more than 0.07 wt. % Al, not more than 0.02 wt. % N, not more than 0.01 wt. % O, and C and N in the conditions satisfying N(wt. %)/C(wt. %).gtoreq.2 and 0.006.ltoreq.[C(wt. %)+N(wt. %)].ltoreq.0.025, and further Ti in the conditions satisfying {Ti(wt. %)-2.times.S(wt. %)-3.times.O(wt. %)}/[C(wt. %)+N(wt. %)].gtoreq.4 and [Ti(wt. %)].times.[N(wt. %).ltoreq.30.times.10.sup.-4.
However, in these techniques, when a severe deep drawing work is carried out, ridging occurs and thus they cannot say sufficient techniques. Also, there is a problem that the occurrence of a nonuniform deformation at a drawing work is not improved.
On the other hand, as a technique of improving the anisotropy of the plastic strain ratio, a ferritic stainless steel containing not more than 0.03 wt. % C, not more than 1.0 wt. % Si, not more than 1.0 wt. % Mn, not more than 0.05 wt. % P, not more than 0.015 wt. % S, not more than 0.1 wt. % Al, not more than 0.02 wt. % N, from 5 to 60 wt. % Cr, from 4.times.(C+N) to 0.5 wt. % Ti, from 0.003 to 0.02 wt. % Nb, and from 0.0002 to 0.005 wt. % B or further containing at least one kind of from 0.0005 to 0.01 wt. % Ca and from 0.1 to 5.0 wt. % Mo is disclosed in (e) Patent Publication (unexamined) No. 8-20843.
By the technique, certainly, Ar becomes about 0.15 or lower and the anisotropy is improved but the anti-ridging property is insufficient.
Also, techniques of improving the deep drawability are disclosed in (f) Patent Publication (unexamined) No. 8-260106 and (g) Patent Publication 8-26436.
In the above-described (f), by adding a slight amount of Nb, .DELTA.r is reduced and further by adding V, the yield ratio is lowered and in the above-described (g), by making appropriate the addition amounts of Ti, Nb, and B, the drawability and the surface characteristics are improved.
However, it is hard to say that both the techniques are the techniques of sufficiently satisfying the workability and further, in the portions subjected to a severe deep drawing work, the problem of the generation of ridging is not sufficiently improved.
As described above, in the ferritic stainless steels by the conventional techniques, the deep drawability and the anti-ridging property have not yet been improved to a sufficient level and particularly, when a severe deep drawing work is applied, there is a problem that ridging occurs.
In view of the circumstances of the conventional techniques, an object of the present invention is to provide a ferritic stainless steel plate having both the improved deep drawability and the improved anti-ridging property at a deep drawing work and a production technique thereof.
Also, other object of the present invention is to provide a ferritic stainless steel plate having the deep drawability satisfying the characteristics of the r value of not less than 1.8 and .DELTA.r of not more than 0.15 and having the excellent anti-ridging property, and the production technique thereof.